The use of liquid nitrogen for quick and easy cryogenicc milling of fruit and vegetablee samples. WESSLING Group, Germany

Transcription

1 The use of liquid nitrogen for quick and easy cryogenicc milling of fruit and vegetablee samples Dr. Manol Roussev WESSLING Group, Germany

2 Are we setting the proper priorities?

3 Getting straight to the (quality) point sampling and sample preparation underestimated? an often neglected but crucial topic * If collected samples [ ] do not adequately represent the actual lot [ ], then all costs, time and efforts [ ] are wasted and can actually yield misleading results * *Stephen J Lehotay, Jo Marie Cook : J. Agr. Food Chem.63 (18) Feb 2015

4 The most important topic for analysis Quality requirements for sample preparation (e. g. SANTE/11945/2015)

5 Extraction efficiency vs. particle size To improve the extraction efficiency of low moisture commodities (e.g. cereals, spices, dried herbs), it is recommended that small particle sizes, preferably less than 1 mm, are obtained. (S SANTE/11945/2015)

6 Degradation rate vs. temperature comminution [ ] at ambient temperature has a significant influence on the degradation of certain pesticide residues (SANTE/11945/2015)

7 Volatility and instability of pesticides Milling should be performed in a way that avoids exten- as heat can cause losses of certain sive heating of the samples, pesticides. (SANTE/11945/2015)

8 Communition: how should we proceed? Cutting and homogenization - at ambient temperature? - under cryogenicc conditions? Fine milling and cooling are absolutely essential

9 (Common) cryogenic techniques Cryogenic milling using dry ice Dry ice : a practical and fast comminution method? common sense? However: must cool down first; mill subsequently losses when stored Alternatives?

10 Liquid nitrogen: a dry ice alternative?

11 Reservations regarding liquid nitrogen Liquid nitrogen is? dangerous not applicable in daily routine inappropriate not available

12 LN 2 : Follow the safety guidelines! well ventilated rooms prevent asphyxiation LN 2 equipment must be kept clear of combustible materials use only approved containers eye/face protection / skin protection insulated gloves should be loose-fitting

13 Liquid nitrogen: (easy) equipment

14 Main advantages of liquid nitrogen no freezing sampless before comminution evenly distributed in test samples no condensation within sample processing can be continued immediately

15 The use of LN2: just quick and easy? Not only is the use of LN 2 applicable to fruit and vegetables but it is also versatilely applica able to all food and feed samples in the laboratory routine

16 The use of LN2: just quick and easy? Further advantages (I): (I) Samples become quickly brittle: liquid physical state of LN2 leads to immediate and homogenous freezing distribution High sugar and low water containing commodities (e.g. raisins) don t become sticky and build clumps. On the contrary, they become free-flowing and powdery

17 The use of LN2: just quick and easy? Further advantages (II): LN 2 causes cells to burst immediately (samples don t need to be frozen prior to milling): high extraction efficiency Hard commodities (cocoa beans) and complex matrices easily comminutible Highly efficient

18 Dithiocarbamates and comminution SANTE requirements: Where comminution is known to affect residues (e.g. dithiocarbamates ) the test portion should consist of whole units of the commodity, or segments removed from large units. To our surprise

19 Losses of dithiocarbamates during milling Using liquid nitrogen: Despite milling the entire sample there are hardly any losses of Thiram Low temperature conditions are obviously prerequisite

20 Proficiency test as proof Design of proficiency test P1510-MRT : Strawberry homogenate CS 2 (Thiram) was spiked with 0,4 mg/kg Test materials were co ooled with liquid nitrogen during the entire sample preparation Homogeniety testing using LN2: recovery of the spiked level: 95 % (Thiram)

21 For comparison: DTC in lettuce [mg/kg] spiked level assigned level DTC-high, test material spiked at ambient temperature Mean recovery of the spiked level: 13 % 0,08 0,07 0,06 0,05 0,04 0,03 0,02 0,01 0 spiked level assigned level DTC-low, test material spiked by using dry ice Mean recovery of the spiked level: 30 % Method performance assessment: Dithiocarbamates [ ] in lettuce purée samples; Lach & Bruns, Consulting chemists (Hamburg, Germany), January 2012

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23 Dithiocarbamates in strawberries [mg/kg] 0,45 0,4 0,35 0,3 0,25 0,2 0,15 0,1 0,05 0 spiked level assigned level own laboratory DTC: test material spiked using liquid nitrogen Mean recovery: 76 % Own recovery: 93 %

24 The use of liquid nitrogenn allows a modification for cryogenic comminution of the entire sample by determination of dithio ocarbamates as CS 2 leads to Thiram recoveries of up to 95 %

25 Quality requirements I (SANTE) [ ] it is recommended that the samples are homogenised at low temperature (e.g. frozen and/or in the presence of dry ice )

26 Quality requirements II (SANTE) To improve the extraction efficiency of low moisture commodities, it is recommended that small particle sizes, preferably less than 1 mm, are obtained.

27 Quality requirements III (SANTE) Where comminution is known to affect residues (e.g. dithiocarbamates ) the test portion should consist of whole units of the commodity, or segments removed from large units. Should cryogenic milling the entiree sample using LN2 be added to SANTE??

28 Lifting the curtain

29 Putting it all in a nutshell Cryogenic milling using liquid nitrogen quick and easy sample processing cheap equipment highly efficient / rugged and safe excellent comminution of complex matrices fine particle size (<< 1000 µm) no degradation during recoveries of Thiram!) homogenization (best

30 Just to joke Cryogenic milling using liquid nitrogen Quick and Easy sample processing Cheap equipment highly Efficient / Rugged and Safe QuEChERS of comminution

31 Σας ευχαριστώ πολύ για την φιλο οξενία σας